I can only speak of this from the other side of the easel. I have been working with models since college. I have had an art studio and have worked with many models. Some are good, some, not so much. Best ones I have worked with were dancers who were quite tone and were able to stay quite still for 20-40min at a time. One or two models have let me be nude as well. I have asked first and we have discussed nudism.